Grinding machine



May 8, 1962 G. H. LOCKWOOD GRINDING MACHINE 2 Sheets-Sheet 1 Filed March22, 1960 gm ITTJQQDODQQQQQQQ FIG. I.

GEURGEHLOCKWOOD INVENTOR.

ATTD EY May 8, 1962 s. H. LOCKWOOD GRINDING MACHINE Filed March 22, 19602 Sheets-Sheet 2 FIG. 2.

GEORGE H. LOOK WOOD INVENTOR.

A T TORNE Y United States Patent 3,032,935 GRINDING MACHINE George H.Lockwood, Worcester, Mass, assignor to The Heald Machine Company,Worcester, Mass, a corporation of Delaware Filed Mar. 22, 1960, Ser. No.16,853 Claims. (Cl. 51-103) This invention relates to a grinding machineand more particularly to apparatus arranged to finish surfaces ofrevolution by abrasion.

It has long been recognized in the internal grinding art that one of thebiggest difficultien encountered is that the outside surface may callfor a finish tolerance which is much greater than that of the internalbore. When this is true and the workpiece is supported on this outersurface, as is common during centerless grinding, considerabledifliculty is encountered in providing an internal surface finished to avery close tolerance. It has also been recognized that a high degree of0D. compensation (which is the term used to indicate methods used tocompensate for variations in the dimensions of the outside diameter of aworkpiece) is obtained by using a V-type shoe support so that the centerline of the workpiece varies from piece to piece along the vertical linebisecting the V in a vertical direction. This is used, naturally, whenthe feed of the abrasive wheel into the work is intended to be in ahorizontal direction; it can be readily seen that large amounts ofvertical movement due to variations in OD. produce with such anarrangement very little lateral motion of the center line. Variousdifiiculties are encountered, however, when one attempts to put theV-type support concept into a practical application. For one thing,since the pressure of the wheel on the internal surface is in a lateraldirection at a point well above the shoes, there is a tendency for thegrinding wheel to roll the workpiece out of the support; it then becomesnecessary to use a pressure wheel on the side of the workpiece oppositethe supporting shoes or to use a third support opposite the grindingwheel, this last method being indicated in the patent to Quimby lt-2,758,427. This patent, however, shows a third shoe which, although itis adjustable from piece to-piece, is fixed, so far as any individualworkpiece is concerned. These and other limitations and difficultiesexperienced with the prior art devices have been obviated in a novelmanner by the present invention.

It is, therefore, an outstanding object of the invention to provide agrinding machine in which automatic compensation is made for OD.variations and the workpiece is suitably supported during grinding.

Another object of this invention is the provision of an internalgrinding machine in which a shoe is pressed against the outside surfaceof the workpiece at a point generally opposite the pressure of the wheelon the internal surface, the said shoe providing a force almost exactlyequaling that of the wheel.

A further object of the present invention is the provision of aninternal grinding machine in which a shoe presses against the outsidediameter and moves toward and away from a predetermined location inaccordance with the variations in the outside diameter of the Workpiece.

It is another object of the instant invention to provide a grindingmachine including a novel means for bringing about drag on the workpiecewhich is proportional to the drag caused by the grinding wheel force.

It is a further object of the invention to provide an internal grindingmachine having a V-type shoe support including automatic O.D.compensation, having a third 3,032,935 Patented May 8, 1962 ice shoewhose location varies automatically with vairations in O.D., whichpresses against the external surface of the workpiece with a forceexactly equal and opposite to the grinding wheel force.

A still further object of this invention is the provision of a feed-rategrinding machine for internal grinding in which an exterior shoe pressesagainst the workpiece with a force equal and opposite to the forceexerted against the internal surface by the abrasive wheel.

It is a still further object of the present invention to provide acontrolled-force grinding machine for internal grinding in which apressure shoe exerts on the outside diameter a force equal and oppositeto that presented against the inside surface by the abrasive wheel.

Another object of the invention is the provision of an internal grindingmachine in which distortion due to wheel pressure is reduced to aminimum.

Another object of the invention is the provision of an internal grindingmachine of the shoe centerless type, wherein the workpiece is maintainedinthe shoes by the. use of an eccentric drive plate and wherein means isprovided for providing a friction drag on the exterior surface of theworkpiece which prevents the workpiece from leaving the shoes when veryhigh grinding forces are used.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

The character of the invention, however, may be best understood byreference to certain of its structural forms, as illustrated by theaccompanying drawings in which:

FIG. 1 is a schematic view of the grinding machine. embodying theprinciples of the present invention; and

FIG. 2 is a schematic view of another grinding machine making use of thepresent invention.

In general terms, the present invention consists in providing a grindingmachine for finishing the surface of a bore in a workpiece in which abase is provided and a workhead is fixed to the base, which workhead isadapted to support the workpiece for rotation about the axis of thebore; a wheelhead mounted on the base is provided for feeding movementtransversely of the axis of the workpiece rotation and a wheel isrotatably mounted on this wheelhead for abrasive contact with thesurface of the bore; an actuator is provided for furnishing the saidfeeding movement and a pressure member is provided which is adapted tocontact the outer surface of the workpiece in the general area ofintersection thereof with a radial line extending from the axis of thebore through the point of contact of the wheel with the surface of thebore; then, means is provided to cause the force on the outer surface ofthe workpiece produced by the pressure member to be substantially equalto the force produced by the wheel upon the inner surface of theworkpiece,

In FIG. 1 is shown a schematic view of a controlledforce grindingmachine making use of the principles of the invention. The grindingmachine, indicated generally by the reference numeral 10', is of thegeneral type shown in the patent to Hahn No. 2,647,348 in which thecontrolled element in feeding is the force of the grinding wheel againstthe surface to be finished, the rate of feeding varying during theprocess as is required to maintain the predetermined force. The grindingmachine is provided with a base 11 on which is mounted a workhead 12 anda wheelhead 1-3. The wheelhead is mounted on a wheelhead table 14,which, in turn, is mounted on the base 11, there being anti-frictionelements 15 interposed .between the two to provide for smooth movementof the wheelhead table over the base 11 in a transverse direction. Anactuator 16 of the linear type is included in a feed box 17, which formspart of the base 11; the piston 18, which is joined to the wheelheadtable 14 by means of a piston rod 19, serves to join the wheelhead table14 to the base 11 and to provide for relative motion therebetween. Thewheelhead 13 includes an electric motor 21 which drives a wheel spindle22 on which is mounted an abrasive wheel 23. The workhead 12 includes apair of shoes 24 and 25 on which are mounted a workpiece 26 having abore or inside surface 27 which is to he finished by abrasion and anoutside cylindrical surface 28 which presumably has already beencompletely finished. The shoes 24 and 25 are provided with arcuatesurfaces for contacting the outside surface 28 of the workpiece in amanner similar to the shoes shown and described in the patent to Blood,Reissue No. 24,202. Furthermore, means is provided associated wtih theworkhead 12 for driving the workpiece, this consisting of a drive plate(not shown) contacting one end of the workpiece, and another means (notshown) for producing a pressure on the workpiece in the axial directionagainst this drive plate, all in a manner similar to that described inthe Blood patent mentioned hereinabove. The drive plate is locatedeccentrically of the centerline of the workpiece so that there is acomponent of slip friction force in the direction of the shoes to holdthe workpiece in the shoes 24 and 25.

Mounted in the workhead 12 is a cylinder 29 in which is slidably mounteda piston 31. The piston 31 is provided at one end with a reduced portion32 and at the other end with a button 33. A cap 34 is bolted over theopening of the cylinder and limits the outward motion of the piston 31.Also mounted on the workhead 12 is a lever 35 which is attached to theworkhead at one end by a pivot pin 36 for swinging motion in a plane ata right angle to the axis of the workpiece. At the end opposite thepivot pin 36 the lever 35 is provided with a contacting finger 37adapted to engage the button 33 on the piston 31. At an intermediatepoint between the pivot pin 36 and the finger 37, but related moreclosely to the pivot pin 36, the lever is provided with a finger '38.Fastened at one end to the workhead 12 is a reed 39, at the other end ofwhich is fastened a supporting shoe 41 which lies between the finger 38on the lever 35 and the outer surface 28 of the workpiece 26. Thesurface of the supporting shoe 41 which contacts the workpiece is curvedin the same manner as the shoes 24 and 25 so as to have a curvatureequal to the average radius of the workpiece. A hydraulic line 42connects the outer end of the cylinder 29 to the outer end of thecylinder 17 of the linear actuator 16. A hydraulic line 43 connects theline 42 to the output side of a pressure regulating valve 44, which, inturn, is connected by a line 45 to a source of hydraulic pressure (notshown).

The operation of the invention will now be readily understood in view ofthe above description. Since the grinding machine is of thecontrolled-force type, the abrasive wheel 23 will be pressed into theinner surface 27 of the workpiece 26 in such a manner that the forceonly will be controlled. Usually this is done to provide the greatestgrinding force commensurate with long life of the wheel and properfinished surface of the workpiece, but at the same time great enough toprovide the shortest grinding cycle. By providing oil pressure throughthe line 45 and the pressure regulating valve 44 into theline 43 and theline 42, hydraulic fluid is introduced into the cylinder 17 and movesthe piston rod 19 to the right, thus causing the wheelhead table 14 tomove to the right relative to the base 19 and carry the motor 21 and thewheel 23 laterally relative to the workpiece 26. The grinding force, ofcourse, will be determined by the pressure of the oil in the cylinder 17multiplied by the area of the piston 18.

The workhead 12 drives the workpiece 26 and rotates it,

and the slight eccentricity between the workpiece and the driving plateforces the workpiece downwardly into the shoes 24 and 25. As variationsoccur from-piece to piece in the CD. of the .outer surface 28, theworkpieces will ride higher or lower in the shoes 24 and 25, thecenterlines of succeeding workpieces moving along a vertical linepassing through this centerline. This means that the horizontal distanceof the inside surface 27 from the centerline of the workpiece will notvary appreciably and it will be relatively easy to bring about a properdimension on the inside surface 27. The hydraulic pressure which is feltby the cylinder 17 also passes through the line 42 into the cylinder 29and presses against the outboard end of the piston 31 moving it to theleft. The movement of the piston 31 to the left causes its button 33 tocontact the finger 37 on the lever 35, thus rotating it counterclockwiseabout the pivot pin 36. This causes the finger 38 to press against theouter side of the shoe 41 which is supported by the reed 39 so that theshoe moves toward the workpiece and contacts the outside surface 28. Ina practical embodiment of the invention, the location of the finger 37and the finger 38 on the lever 35 relative to the pivot pin was in theratio of 5 to 1, thus providing a second degree lever having that forceratio. It can be seen, also, that the pressure of the shoe 41 is in apredetermined ratio to the pressure of the Wheel 23 on the opposite sideof the workpiece 26. Actually, the shoe 41 is arranged so that it lieson the same horizontal line with the axis of the spindle 22 and of thewheel 23. It can be seen that the shoe 41 not only moves inwardly andoutwardly to compensate for variations in the location of the outsidesurface 28 of the workpiece, due to variations in OD, but it alsochanges its force characteristic on that surface as the force changes onthe wheel 23. It will be understood that, in the high-force grinding ofthe type used, the control element in the grinding machine is thegrinding force rather than the feed rate. Such a high force between thewheel and the workpiece provides rotation of the workpiece until undercertain conditions it reaches almost the same speed as the wheel itself;this has the effect of reducing the relative slip between the drivingplate and the end of the workpiece and, therefore, reducing thecomponent of force which tends to press the workpiece downwardly intothe shoes. By use of the present invention, the shoe 41 provides a dragon the surface of the workpiece which is proportional and opposed to thedriving force on the inside caused by the wheel 23; this has the effectof maintaining the rotation of the workpiece at a speed slower than thedriving plate in an amount sufficient to bring about the required forceto hold the workpiece in the shoes. This obviates in many cases the needfor a roller pressing on the upper periphery of the workpiece to hold itin the shoes. Furthermore, as is well known, it is desirable that thelinear speed of the workpiece be substantially less than that of thewheel, but without the drag provided by the shoe 41 the above describedtendency of the workpiece in high force grinding to reach the peripheralspeed of the wheel provids an incorrect ratio between the peripheralspeeds of the two elements so that the abrading action is lessefficient. This drag, incidentally, is proportional to the grindingwheel force; this is a desirable feature, since it is not a good idea tohave the drag force higher than is needed.

FIG. 2 shows schematically the application of the invention to afeed-rate grinding machine wherein the feeding of the wheel into theworkpiece is at a preselected rate of travel and the forces encounteredbetween the wheel and the workpiece fall in an uncontrolled manner in awide range of values in a given cycle of operation. The grindingmachine, indicated generally by the reference numeral 110, is of thefeed-rate type which is well known and which is shown in theabove-mentioned patent of Blood, Reissue No. 24,202. The machine isprovided with a base 111 on which is fixed a workhead 112. Mounted onthe base 111 is a wheelhead 113 mounted on a wheelhead table 114; thetable, in turn, is mounted on the base 111 for transverse slidingmovement, there being anti-friction elements 115 interposed between thetwo. An actuator 116 of the linear type is mounted in a feed box 117.The feed box is of the type shown and described in the patentapplication of Lockwood et al. Serial Number 833,204, filed August 12,1959. The linear actuator, which is hydraulically driven, is providedwith a piston rod 118' formed as a rack which engages a gear 119 mountedon a feed screw 120 suitably mounted in bearings in the base 111. Thefeed screw engages a nut forming part of the wheelhead table 114 and, byits rotation, causes movement of the wheelhead table across the base111. An electric motor 121 forms part of the wheelhead 113 and drives awheel spindle 122 on which is mounted an abrasive wheel 123.

The workhead 112 is provided with shoes 124 and 125 holding a tubularworkpiece 126 having an inside surface 127 and an outside surface 128.Also provided in the workhead is a cylinder 129 in which is mounted apiston 131 having at one end a reduced portion 132 and at the other enda button 133. A cap 134 overlies the cylinder and limits thelongitudinal motion of the piston 131. Also mounted on the workhead 112is a lever 135 connected at its lower end to the workhead by means of apivot pin 136. At its upper end the lever is provided with a finger 137and an intermediate portion closely adjacent to the pivot pin 136 isalso provided with a finger 138 located on the opposite side of thelever from the finger 137. Also mounted on the workhead 112 is a reed139 which hanges vertically and has at its lower free end a supportingshoe 141. The shoe 141 as well as the shoes 124 and 125 are suitablyarcuately formed to provide contact with the outer surface 128 of theworkpiece 126 in the manner shown and described in the above-mentionedreissue patent of Blood No. 24,202. A hydraulic line 142 is connected atone end to the cylinder 129 and at the other end to the output side of aservo regulator 143. This servo regulator may be of the well-known type,such as shown in Patent No. 2,767,609, which provides a hydraulicpressure proportional to an electrical input signal. The regulator isconnected by a line 144 to a source of hydraulic pressure (not shown).The servo regulator 143 is connected by an electrical line 145 to aload-sensing control 146. This load-sensing control is of the type shownin the patent to Dunigan No. 2,722,648 and has the attribute of giving asignal proportional to the load in a three-phase alternating currentmotor similar to the motor 121 used in the machine. The load-sensingcontrol is connected by three-phase lines 147 to the motor 121 and alsoconnected to an electrical power source (not shown). The loadsensingcontrol 146 is connected to the line 145 to supply it with an electricalsignal which at all times is proportional to the load on the wheelmotor.

The operation of this apparatus is very similar to that described inconnection with FIG. 1. Hydraulic pressure provided to the linearactuator 116 is controlled by the elements in the feed box so that feedtakes place according to a pre-arranged cycle and, therefore, the feedscrew 120 is similarly rotated to move the wheel 123 into the innersurface 127 of the workpiece 126 to provide an abrading action. Thegrinding wheel is driven by the motor 121 whose load is continuouslysensed by the control 146. An electrical signal proportional to the loadon the motor 121 passes through the line 145 to the servo regulator 143;the regulator causes the pressure passing from the line 144 into theline 142 to be proportional to the signal received and this pressure,therefore, is proportional to the load on the motor. The load on themotor is also proportional to the pressure between the wheel 123 and theworkpiece 126, this pressure being the grinding force, so-called. Thismeans that the pressure in the line 142 will also be proportional to thegrinding force and the hydraulic pressure in the line 142 acts on thepiston 131. The force is transmitted through the lever 135 on thesupporting shoe 141 so that it presses against the outer surface 128 ofthe workpiece. In this way it can be seen that the pressure on theoutside of the workpiece provided by the shoe 141 is at all times equalto the pressure on the inside of the workpiece provided by the abrasivewheel 123, this being the desired result.

Most of the advantages enumerated above in connection with thecontrolled-force grinding machine are obtained when the invention isused with a feed-rate grinding machine. For instance, at times duringthe feed-rate cycle, the grinding force becomes quite high and a drag inthe opposite direction to the rotating force of the wheel on theworkpiece is desirable and is provided in this case by the shoe 141. Inthe same way, the pressure of the wheel tends to rock the workpiece outof the shoes 124 and and the pressure of the shoe 141 prevents this.

It will be understood, of course, that in the above description theapplicant has omitted many necessary or desirable elements of a grindingmachine which, however, are not part of the invention. For instance, itis necessary to provide a workhead and driving plate to engage one endof the workpiece; a clamping plate may be provided at the other end ofthe workpiece or a pressure roll may engage the periphery of theworkpiece opposite the shoes. It will also be necessary to provide foraxial movement of the wheel into the bore of the workpiece.

it is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form shown and described, but it is desired to include all such asproperly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent, is:

l. A grinding machine for finishing a surface of revolution of aworkpiece, comprising a base, a workhead mounted on the base and adaptedto support the workpiece for rotation about the axis of the surface, awheelhead mounted on the base, means for bringing about feeding movementof the wheelhead and workhead relative to each other transversely of theaxis of workpiece rotation, a wheel rotatably mounted on the wheelheadand adapted to contact the said surface, an actuator for bringing aboutthe said feeding movement, a pressure member adapted to contact asurface of the workpiece in the area of intersection of the surface witha line extending from the axis of the workpiece through the point ofcontact of the wheel with the said surface, and means to cause the forceon the workpiece produced by the pressure member to be substantiallyequal to the force produced by the wheel on the said surface.

2. A grinding machine for finishing a surface of a bore in a workpiece,comprising a base, a workhead mounted on the base and adapted to supportthe workpiece for rotation about the axis of the bore, a wheelheadmounted on the base for feeding movement transversely of the axis ofworkpiece rotation, a wheel rotatably mounted on the wheelhead andadapted to contact the surface of the bore, a linear actuator forbringing about the said feeding movement, a pressure member adapted tocontact the outer surface of the workpiece in the area of intersectionthereof with a radial line extending from the axis of the bore throughthe point of contact of the wheel with the surface of the bore, andmeans to cause the force on the Outer surface of the workpiece producedby the pressure member to be substantially equal to the force producedby the wheel on the surface of the bore.

3. A grinding machine for finishing the surface of a bore in a workpiecehaving an external surface of revolution, comprising a base, a workheadmounted on the base, two shoes adapted to support the workpiece bycontact with the external surface, the shoes being arranged to form aV-shaped support for rotation of the workpiece about the axis of thebore, a wheelhead mounted on the base for feeding movement transverselyof the axis of the workpiece rotation, a wheel rotatably mounted on thewheelhead and adapted to contact the surface of the bore, a linearactuator for bringing about the said feeding movement, a third shoeadapted to contact the outer surface of the' workpiece in the area ofintersection thereof with a radial line extending from the axis of thebore through the point of contact of the wheel with the surface of thebore, and means to cause the force on the outer surface of the workpieceproduced by the pressure member to be substantially equal to the forceproduced by the wheel on the surface of the bore.

4. A grinding machine for finishing a surface of revolution of aworkpiece, comprising a base, a workhead mounted on the base, two shoesadapted to support the workpiece by contact with an external surface ofrevolution, the shoes being arranged to form a V-shaped support forrotation of the workpiece about the axis of the surface of revolution, awheelhead mounted on the base, means for bringing about feeding movementof the wheelhead and workhead relative to each other transversely of theaxis of workpiece rotation, a wheel rotatably mounted on the wheelheadand adapted to contact the said surface, an acutator for the saidfeeding movement, a third shoe adapted to contact the workpiece in thearea of intersection thereof with a radial line extending from the axisof the bore through the point of contact of the wheel win the saidsurface, and means to cause the force on the workpiece produced by thepressure member to be substantially equal to the force produced by thewheel on the said surface.

5. A controlled-force grinding machine for finishing a surface ofrevolution of a workpiece, comprising a base, a workhead mounted on thebase and adapted to support the workpiece for rotation about the axis ofthe surface, a wheelhead mounted on the base, means for bringing aboutthe feeding movement of the workhead and wheelhead relative to eachother transversely of the axis of workpiece rotation, a wheel rotatablymounted on the wheel head and adapted to contact the said surface, afirst hydraulic cylinder for bringing about the said feeding movement,means providing hydraulic fluid under pressure to the cylinder, apressure member adapted to contact the workpiece in the area ofintersection thereof with a radial line extending from the axis of thebore through the point of contact of the wheel with the said surface, asecond hydraulic cylinder actuating the pressure member and receivinghydraulic fluid under pressure from the same means as the firstcylinder, the second cylinder causing the force on the workpieceproduced by the pressure member to be substantially equal to the forceproduced by the Wheel on the said surface.

6. A controlled-force grinding machine for finishing the surface of abore in a workpiece, comprising a base, a workhead mounted on the baseand adapted to support the workpiece for rotation about the axis of thebore, a wheelhead mounted on the base for feeding movement transverselyof the axis of workpiece rotation, a wheel rotatably mounted on thewheelhead and adapted to contact the surface of the bore, a firsthydraulic cylinder for bringing about the said feeding movement, meansproviding hydraulic fluid under pressure to the cylinder, 2. pressuremember adapted to contact the outer surface of the workpiece in the areaof intersection thereof with a radial line extending from the axis ofthe bore through the point of contact of the wheel with the surface ofthe bore, a second hydraulic cylinder actuating the pressure member andreceiving hydraulic fluid under pressure from the same means as thefirst cylinder, the second cylinder causing the force on the outersurface of the workpiece produced by the pressure member to besubstantially equal to the force produced by the wheel on the surface ofthe bore.

7. A controlled-force grinding machine for finishing the surface of abore in a workpiece having an external surface of revolution, comprisinga base, a workhead mounted on the base, two shoes adapted to support theworkpiece by contact with the external. surface, the shoes beingarranged to form a V-shaped support for rotation of the workpiece aboutthe axis of the bore, a wheelhead mounted on the base for feedingmovement transversely of the axis of workpiece rotation, a wheelrotatably mounted on the wheelhead and adapted to contact the surface ofthe bore, a first hydraulic cylinder for bringing about the saidfeeding, movement,.means providing hydraulic fluid under pressure. to:the cylinder, a third shoe adapted to contact the outer surface of theworkpiece in the areaof intersection thereof with a radial lineextendingfrom the axis of the bore through the point of contact ofthewheel with the surface of the bore, a second hydraulic cylinderactuating the pressure member and receiving hydraulic fluid underpressure from the same means as the first cylinder, the second cylindercausing the force on the outer surface of the workpiece produced by thepressure member to be substantially equal to the force produced by thewheel on the surface of the bore.

8. A feed-rate grinding machine for finishing a surface ofirevolution ofa workpiece, comprising a base, a workhead mounted on the base andadapted to support the workpiece for rotation. about the axis of thesurface, a :heelhead mounted on the base, means for bringing aboutfeeding movement of the wheelhead and workhead relative to each othertransversely of the axis of workpiece rotation, a Wheel rotatablymounted on the wheelhead and adapted to contact the said surface, anelectric motor driving the wheel, an actuator for bringing about thesaid feeding movement, a pressure member adapted to contact theworkpiece in the area of intersection thereof with a radial lineextending from the axis of the bore through the point of contact of thewheel with the said surface, a hydraulic cylinder actuating the pressuremember, a servo regulator supplying hydraulic fluid under pressure tothe cylinder, a control which senses the load on the electric motor andtransmits a signal indicative thereof to the servo regulator, so thatthe force on the workpiece produced by the pressure member issubstantially equal to the force produced by the wheel on the saidsurface.

97 A feed-rate grinding machine for finishing the surface of a bore in aworkpiece, comprising a base, a workhead mounted on the base .andadapted to support the workpiece for rotation about the axis of thebore, a wheelhead mounted on the base for feeding movement transverselyof the axis of workpiece rotation, a wheel rotatably mounted on thewheelhead and adapted to contact the surface of the bore, an electricmotor for driving the wheel, an actuator for bringing about the saidfeeding movement, a pressure member adapted to contact the outer surfaceof the workpiece in the area of intersection thereof with a radial lineextending from the axis of the bore through the point of contact of thewheel with the surface of the bore, a hydraulic cylinder actuating thepressure member, a servo regulator supplying hydraulic fluid underpressure to the cylinder, a control which senses the load on theelectric motor and transmits a signal indicative thereof to the servoregulator so that the force on the outer surface of the Workpieceproduced by the pressure member is substantially equai to'the forceproduced by the Wheel on the surface of the bore.

10. A feed-rate grinding machine for finishing the surface of a bore ina workpiece having an external surface of revolution, comprising a base,a workhead mounted on the base, two shoes adapted to support theworkpiece by contact with the external surface, the shoes being arrangedto form a V-shaped support permitting rotation of, the workpiece aboutthe axis of the bore, a wheelhead mounted on the base for feedingmovement transversely of the axis of workpiece rotation, a wheelrotatably mounted on the wheelhead and adapted to contact the surface ofthe bore, an electric motor driving the wheel, a linear actuator forbringing about the said feeding movement, a third shoe adapted tocontact the outer surface of the workpiece in the area of intersectionthereof with a radial line extending from the axis of the bore throughthe point of contact of the wheel with the surface of the bore, ahydraulic cylinder actuating the pressure member, a servo regulatorsupplying the hydraulic fluid under pressure to the cylinder, 21 controlwhich senses the load on the electric motor and transmits a signalindicative thereof to the servo regulator, so that the force on theouter surface of the Workpiece produced by the pressure member issubstantially equal to the force produced by the wheel on the surface ofthe bore.

References Cited in the file of this patent UNITED STATES PATENTS2,603,043 Bontemps July 15, 1952 5 2,909,009 Schmidt Oct. 20, 19592,923,106 Reusser Feb. 2, 1960

